Hey @tommytcchan Good question!
First thing is that Marvel isn't just the iPhone app, it's an simple and powerful web app too (www.marvelapp.com).
Not only can you do full prototyping on your iPhone just like POP but you can also:
- Create iPad AND iPhone 4/5 demos using our iPhone app.
- You can import PSDs on Dropbox right into the iPhone app to use (or any other image) and we poll those files for changes so that your prototype always stays update
- Everything you do is synced with your web account so your prototype is available there too. Our web app gives you the ability to add fixed headers/footers, embed your prototype onto any blog or site AND create website prototypes (or any screen size)
- You can also download your prototype as a ZIP file containing all the HTML/JS/CSS to run offline or on your own server
- Tons of other stuff and more planned :)
So the iPhone app is just a small part of the ecosystem we're building.
We've just integrated with Placeit too